The aim of the present invention is a method for coating yarn, including steps in which the yarn is first placed in contact with a dispersion of the coating agent in a dispersing agent or with the coating agent in melted form, optionally excess dispersion or melt is scraped back off the yarn, and then the coating is formed on the yarn, where in the case of the dispersion this occurs by means of at least partially removing the dispersing agent by heating, and the yarn thus coated is then cooled down and wound.
Such a method is known. For example, U.S. Pat. No. 3,407,092 describes such a coated yarn that is obtained by guiding a nylon yarn through a bath of an emulsion containing an acrylate-based copolymer in aqueous emulsion and then drying for two minutes at about 93° C. This yarn is then cooled and twisted. About 1 to 10 wt. %. coating agent is applied to the yarns of U.S. Pat. No. 3,407,092.
Coating of fabrics such as wovens, knits, paper, and nonwovens is also known. Generally this manner of coating is understood to mean applying a film coating of natural or synthetic materials, as a coating compound, to fabric or backing, with the goal of making them suitable for special requirements or imparting new properties to them, for example for imitation leather, covers, tarpaulins, etc. By combining suitable fabric or backings and coatings, finished products can be obtained with completely new properties, where the fabric is primarily responsible for the mechanical strength of the final product while the applied coating determines the behavior of the material for use against outside influences, such as breathability, burst strength and scratch resistance, lightfastness and chemical resistance, flame retardancy, water resistance, heat resistance, as well as the appearance, such as printing, dyeing, graining, and the particular applicability.
Generally the coating is spread on the backing as a uniformly thick layer using a “doctor knife”. The thickness of the coating is adjusted according to the particular purpose and can be equal to a fraction of a millimeter as well as several millimeters. This way of applying a coating is known to the person skilled in the art, and does not need to be further discussed here.
Regarding formation of the coating, note that good adhesion of the coating to the backing often is only ensured if first a priming coat is applied, using a very small amount of coating. After intermediate drying, the proportionately heavier layer is applied and optionally even a third “finishing layer”, also called a topcoat, is applied (the latter in particular to ensure scratch resistance).
Thus, the process of coating fabrics can certainly consist of several steps, over the course of which often relatively large amounts of coating agent are employed. This generally also additionally includes the fabric production step itself, and so for example production of fabrics from yarns etc.
Thus, it would be desirable if at least part of the coating method could be already carried out in upstream process steps and so, for example, just before the weaving step. Then the coated yarns could be directly processed into coated fabrics, resulting in a uniform and durable coating of the woven material just by application of heat and/or pressure, for example by hot pressing.
It would also be expedient if, for example, a partial coating was already present on the yarns or in the woven material, so that just one or perhaps two coating steps had to be carried out on the finished fabric.
Many attempts have been made to provide the yarns with coatings before they are further processed into fabrics, such as is done, for example, in U.S. Pat. No. 3,407,092 cited above.
Unfortunately, the known methods for coating yarns always have still had drawbacks which have limited their applicability. Thus, often the amount of coating applied to the yarns is too small to be an equivalent replacement for only coating the fabric afterward. Even the amount applied in U.S. Pat. No. 3,407,092, at 1 to 10 wt. %, is too small.
The uniformity of yarns obtained by direct coating often is also often too poor, both with regard to the amount of coating and with regard to the shape of the coated yarns obtained in this manner. Often yarns are obtained that are not uniformly round or flattened, which can be processed further only with difficulty, for example on looms. Of course, this problem arises to a greater extent when large amounts of coating agent are applied.
In addition, the speed of application of the coating on the yarns is also a problem, since first of all at high speeds the applied coating is nonuniform and/or too light, while at low speeds the process is uneconomical. Within the present invention, speed is understood to mean the length of yarn that comes in contact with the coating agent per unit time.